Star clusters betray Milky Way's cannibalistic past

Mar 19, 2020
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"While the universe looks like a static thing when gazing at the night sky, astronomers are able to see large shifts and changes over millions and billions of years."

Jeez, did not know that astronomers lived so long! I got into the wrong field of science!

Seriously, this is interesting work. What is not clear is how half the globular clusters (GCs) could have been derived from only 5 galaxies. Since they were absorbed in the distant past, it seems likely that each of these assimilated galaxies were themselves amalgamations with many GCs. Otherwise, how do you get so many GCs from only 5 galaxies? Since the Milky Way has so many native GCs (nGCs), based on this article, it stands to reason that assimilated galaxies did also.

The data on spin of the clusters is very interesting. One wonders how their spin directions compare with each other. Do all or most of the spinning GCs have "parallel" spins, or do they all spin in highly variable "directions"? Perhaps there are groups that spin with similar direction.

One assumes that the nGCs likely formed around localized high density hydrogen clouds in the early Milky Way, or all are actually acquired , and Forbes just hasn't figured this out. I suspect these nGCs lack spin. Another issue would be the amount of gas in these GCs. Acquired GCs may be more gas poor than nGCs, since the latter should have being drawing gas from the galaxy throughout its life, but the captured ones cannot for some reason. I suspect a lot may depend on their movement through the galaxy (in and out of the plane, or stable).

Finally, if the Milky Way absorbed all those galaxies with all those clusters, I suspect it too was a minor galaxy, and the addition of 5 other galaxies put the combination into the class of giant spiral galaxies. There is clearly more to this story than the Milky Way eating 5 galaxies.
 
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